Synthesis of organic compounds



Nov. 9, 1948. w. e. LOVELL EI'AL 2,453,144

SYNTHESIS OF ORGANIC COMPOUNDS Filed May 3, 1946 [LIME THKE OFF HOPPEk Zrvuwnbomw w 1 whee? G. 0011522;

2220M clmazzjgm J Haw? J11 aaczzzemufaznex Patented Nov. 9, 1948 2,453,144 SYNTHESIS OF ORGANIC COMPOUNDS Wheeler 6. Lovell, Maurice J. Mulligan, and Hart K. Lichtenwalner, Detroit, Mich, assignors to General Motors Corporation, Detroit, Mich, a

corporation of Delaware Application May 3, 1946, Serial No. 667,01t

5 Claims. (Cl. 260-683) The invention relates to a method of synthesizing organic compounds and more particularly to a new method or preparing olefin hydrocarbons, starting with an aliphatic olefin hydrocarbon and adding to it an alkyl group adjacent to the doublc bond so as to produce in one operation another olefin of higher molecular weight. The process is of special advantage in producing. by suitable choice of starting material, olefins of highly branched structure which may be readily hydrogenated to the corresponding paraillns and which have special'usefulness in internal combustion engine fuels because of their freedom from knock.

One object of the present invention is to provide an improved continuous process of producing olefin hydrocarbons starting with an aliphatic olefin hydrocarbon and adding to it an alkyl group adjacent to the double bond so as to produce in one operation an olefin of higher molecular weight.

Another object of the invention is to provide a low pressure, continuous process of producing olefin hydrocarbons starting with tetramethylethylene (2,3-dimethyl-2-butene) and adding an alkyl group adjacent to the double bond so as to produce in one operation an olefin of higher molecular weight having a highly branched structure.

A further object of the invention is to provide a low-pressure process of producing triptene (2,2,3-trimethyl-3-butene) Other objects and advantages of the invention will become moreapparent from the detailed description whichjollows:

One of the features of the present invention comprises carrying out a reaction between tetramethyleth'ylene (2.3-dimethyl-2-butene) and an alkyl halide continuously and at atmospheric or substantially atmospheric pressure in the presence of an alkali to produce a higher olefin containing an additional alkyl group and an alkali halide and water. Methyl chloride, methyl iodide, methyl bromide, ethyl chloride, and isopropyl chloride are suitable alkyl halides. As the alkali we prefer to use quickllme or calcium oxide.

The accompanying drawing illustrates one form of apparatus by means 01 which the process may be carried out in a continuous manner. In the drawing, l0 represents a vertical reaction tube which is charged with calcium oxide or lime by means or a lime feed hopper l2 and plunger l4 operating in sleeve l5. The lime feed hopper and sleeve are preferably heated as, for example, by means of a steam jacket. The tube I0 is surrounded by a heating jacket I 6 whose purpose is ill to bring the reacting mass to a. temperature suitable for reaction, and also, when reaction has been initiated to conduct the heat of reaction away and to keep the temperatures from becoming excessive. Reaction temperatures on the order of 200 C.'to above 300 C. may be employed. The heating medium is maintained at a temperature on the order of 205 C. to 250 C.

The heating medium such as, for example, Dowtherm (eutectic mixture of diphenyl and diphenyl oxide) is heated by an electric heater l8 arranged in a heater tube 20. The heating medium circulates through the heating jacket l6 by natural convection, entering the heating jacket l8 by means of pipe 22 and leaving it through pipe 24. An expansion tank 26 is connected to the heating jacket by means of pipe 28,

In the elongated vertical tube I0 is a rotary shaft 30 carrying a plurality of blades 32 for thoroughly stirring or agitating the lime and other reactants.

The tetramethylethylene (2,3-dimethyl-2-butene) and the alkyl halide in suitable proportions enter the tube I0 adjacent the bottom end thereof through a pipe 34 and are discharged into the lime mass by means of the distributor 38. The mixture of olefin and alkyl halide is preheated and vaporized by means of the U-shaped pipe 38 passing through the heating medium in the heater tube 20. The preheater preferably heats the mixture of olefin and alkyl halide to substantially reaction temperature before it enters the tube l0. At the top of the tube I0 is an outlet 40 for continuous removal of both reacted and unreacted vapors. A suitable condenser 42 is provided to condense the vapors as they are removed. Adjacent the top of the tube I0 is a screen It through which the vapors pass and which substantially prevents the lime from flowing out of the tube with the vapors.

At the bottom end of the tube l0 there is provided a plunger 46 for discharging the reaction products of calcium halide, calcium hydroxide I and unreacted calcium oxide into a lime takeofl. hopper 48. The lime take-oil hopper is preferably heated as, for example. by a steam jacket.

From the above it is apparent that there is a 3 on the rates of introduction of the olefin and alkyl halide and the ratio between the alkyl halide and olefin, and they may be varied over a wide range.

The lime is fed through the reactor In at a rate above about 110% of that theoretically required. The exact proportion is not critical and rates above 200% of the theoretical have been used.

In starting. operation withfresh lime in the reaction tube l there is a period of time in which no reaction takes place. When reaction begins as indicated by a rise'in temperature of the lime mass near the entrance of the vapors and by the products from the tube or column l0, lime is introduced continuously at the top of the column and the solidreactionproducts of calcium halide, calcium hydroxide and unreacted calcium oxide similarly removed continuously from the bottom of the column. Once the reaction has been thus started it goes on indefinitely as long as suitable feeds of lime, 2,3-dimethyl-2-butene'and alkyl halide are maintained and the heat of reaction removed. The reaction mass is continuously agitated by the shaft 30 carrying the blades 32.

The purity of the reactants with respect to some contaminants is of importance. For example, it has been observed that the presence of peroxides in the 2,3-dimethyl-2-butene has an inhibiting effect and it is therefore desirable to remove the same prior to reaction. This may be done by distillation or chemical treatment, as for example, by reaction with sodium. Formation of peroxides may be inhibited by addition of an antioxidant such as hydroquinone, to the base material, such inhibitor having no significant effect on the alkylation reaction. Other antioxidants such as pyrogallol or benzylamino phenyl may be used to prevent peroxide formation.

The feed material may contain a small amount of aromatics such as benzene for example, or a small proportion of other olefins than 2,3-dimethyI-Z-butene.

We prefer to use quicklime or calcium oxide as the alkali because of its availability and cheapness and the fact that it enters into the reaction at a temperature at which the other reactants are in a suitable condition. It has the ad- .vantage that it serves two purposes: one may be thought of as being an absorbent for the hydrogen halide formed in the reaction resulting in the formation of calcium halide and another function being to combine with the water to form calcium hydroxide. We prefer to use calcium oxide rather than calcium hydroxide, conse-' quently, also because the use of the latter requires higher temperatures and such conditions promote the formation of ether and high boiling products. We prefer to use high calcium limes and they have a higher percentage of available calcium oxide. The presence of even very small amounts of active aluminum oxide promotes extensive side reactions. The physical state of the lime is also important in this reaction. We prefer to use limes which have been prepared from the natural carbonate by calcination to the oxide, slaking to the hydroxide, and controlled recalcination to the oxide again; and, in order that the alkylation reaction may be rapid, we prefer that the latter calcination should be carried out so thata small amount, usually below of hydroxide be present in the product. We feel that this amount of hydroxide is not of importance as a chemical individual, but rather as indicating the heat-treatment that the lime has undergone, and the absence of overburning, which we find to be disadvantageous. This is probably related to the physical state of the limev or the extent of surface per unit weight. This may be indicated by the extent to which the absorption of a dye (for example, Sudan 23) takes place from a solvent (such as trimethyl ethylene) on a sample of the lime, and high absorption may be correlated with high activity in the alkylation reaction. We do not wish to be bound by theories as to the relation between the rate of reaction and the particle size of the lime, hydroxide content, purity, and alumina content, but preferto use conditions, such as those mentioned, which conditions we have found to result in a convenient rate of reaction and satisfactory final products.

As a specific example of operation in accordance with the invention, the following detailed description of a process of producing triptene -(2,2,3-trimethyl-3-butene)- continuously at substantially atmospheric pressure from a starting mixture of 2,3-dimethyl-2-butene and methyl chloride will be given. In this example a vertical steel reaction tube l0 five inches in diameter and six feet long is charged with calcium oxide or lime. The tube is surrounded by a heating jacket to heat the reactants and remove heat of reaction as previously described. Into the bottom of the reaction tube is introduced continuously a preheated mixture of methyl chloride and 2,3-dimethyl-2-butene. The ratios of reactants used ranged from three to eight mols of methyl chloride per six mols of 2,3-dimethyl-2-butene. The optimum mol ratio is about 1 to 2. This relatively low ratio favors favorable methyl chloride utilization by keeping the triptene to ether ratio high. Flow rates of the liquid mixture of 2,3-dimethyl- 2-butene and methyl chloride varied from onehalf liter to more than two liters per hours. High feed rates not only increase the capacity of the reactor but also cut down ether formation without effecting triptene production in the same proportion. Lower reaction temperature restricts ether formation.

Under optimum conditions including the low mol ratio of methyl chloride to 2,3-dimethyl-2- butene of about 1 to 2, a relatively high feed rate, and low reaction temperature (under 232 0.), a

. triptene yield of about 25% per pass is obtained,

with 5% of the methyl chloride charged going to ether. With recyling of the unconverted materials, more than of 2,3-dimethyl-2-butene is methylated to triptene, with less than 10% of higher boiling material being formed. With pure 2,3-dimethyl-2-butene, about 75% of the methyl chloride is converted in formation of triptene, with about 10% going to form higher boiling material, and about 10% going to form methyl ether. With methyl pentenes in the feed, the proportion of methyl chloride converted to residue is higher.

After the alkylation has been carried out the triptene or other branched-chain olefin hydrocarbon formed, may be hydrogenated by known hydrogentation processes to produce the corresponding paraffin hydrocarbons characterized by freedom from knock when employed as fuels in internal combustion engines.

We claim:

1. A process of producing an olefin which comprises passing a mixture of 2,3-dimethyl-2-butene and an alkyl halideover fresh lime heated to a temperature within the range of approximately 5 200 C. to 250 C. in an elongated reaction tube at substantially atmospheric pressure until reaction of 2,3-dimethyl-2-butene, alkyl halide and calcium oxide is initiated as indicated by a rise in temperature of the lime mass adjacent the entrance oi the mixture of 2,3-dimethyl-2-butene and the alkyl halide, then introducing fresh lime continuously at one end of the reaction tube and continuously feeding the lime through the reaction tube, continuously passing a mixture of 2,3- dimethyl-2-butene and alkyl halide through the reaction tube in a direction opposite to the direction of flow of lime therethrough, and maintaining the reactants at a temperature within the range of about 200 C. to 300 C. as they pass through the reaction zone, said reactants being at substantially atmospheric pressure as they pass through said reaction tube.

2. A process as in claim 1 in which the alkyl halide is methyl halide. v.

3. A process as in claim 2 in which the methyl halide is methyl chloride.

4. A process as in claim 3 in which the ratio of 6 methyl chloride to 2,3-dimethyl-2-butene is within the range of from three to eight mols of methyl chloride to six mols oi 2,3-dimethyl-2-butene.

5. A process as in claim 1 in which the lime has been prepared by calcination or calcium carbonate to the oxide, slaking the oxide to the hydroxide, and recalcination of the hydroxide to the oxide, said recalcination having been 'stopped short of completion so that a small proportion of hydroxide remains.

WHEELER G. LOVELL MAURICE J. MULLIGAN. HART K. HCH'IENWAINER.

REFERENCES CITED UNITED STATES PATENTS 20 Number Name Date 2,387,596 Marisic Oct. 23, 1945 2,417,119 Miller et al Mar. 11, 194'! 

